Broadband dual-port excited planar lenses

Planar bootlace lenses are frequently used as beamforming networks (BFN) in EW and surveillance systems. They are also being considered for use as low signal level BFN to generate multiple simultaneous beams from low Earth orbiting satellites. The attractions here are the low profile, light weight and compact packaging properties of lens-based BFN. In a previous paper by Chan and Wallace (1990), the design of single-port excited lens was treated. For broadband operation, the single-port excited lens suffers from large ripple level in the power distribution across the array ports as well as high insertion loss at the low end of the operating band. This is caused by the small electrical size of the ports surrounding the lens´ cavity. It should be pointed out that the port width must be kept less than half a guide wavelength at the highest operating frequency to maintain a dominant mode only condition at the feed ports. Otherwise the multi-moded ports would exhibit drop-outs in the power transmission response at certain frequencies in the band. To increase the effective port width, two adjacent ports may be combined with an in-line 3 dB hybrid while maintaining single-mode operation in each port. This is the type of lens we examine.<>